If user doesn't start interacting with page immediately, WP Meteor postpones loading and firing scripts until after page gets rendered, giving you 2x-5x boost in your Pagespeed metric.

This postponement in script loading greatly improves perceived load times for your visitors. It also significantly improves the following important SEO metrics:

In May 2021, Google will incorporate multiple page speed metrics as a search signal in the ranking algorythm

Put all the metrics aside, all that is important is the end user experience. Postponing the scripts improves page render speed no matter what tests say.

  1. If you get rid of 1/3 (that's an average amount of JS on an average WP page) of your page bytes during page load - it definitely helps.
  2. If you don't block page rendering somewhere in the middle by the need to download scripts - it helps even more.
  3. If you don't execute those scripts during page load - you allow all the page elements to render first.

And Google cares about user experience.
And you care about Google's opinion.

Improved Page Speed score is a consequence of better perceived page performance.

As simple as that.
Yes, this mechanics doesn't work everywhere for everyone. But if it doesn't produce artifacts for your site - you're in that lucky bunch of people, who can safely use WP Meteor.

So don't hesitate to install and test, the plugin is made to leave no trace on the disk or in the database upon deactivation and removal.